The present invention relates to rotary fluid pressure devices, and more particularly, to an improved Geroler.RTM. gear set for use therein.
It will become apparent from the subsequent description that the invention is equally adapted for use in any gear set comprising an internally toothed member and an externally toothed member disposed eccentrically within the internally toothed member, in which each of the toothed members rotate about a fixed axis. However, the present invention is especially advantageous when applied to a Geroler.RTM. gear set wherein the axis of the externally toothed member is not fixed, but rather, orbits about the axis of the internally toothed member. Therefore, the present invention will be described in connection with a rotary fluid pressure device utilizing a Geroler.RTM. gear set. It should also be apparent that the present invention may be advantageously applied to a Geroler.RTM. gear set in which the externally toothed member is held stationary, and the internally toothed member orbits and rotates relative thereto.
Geroler.RTM. gear sets (i.e., those in which the teeth of the internally toothed member comprise rollers) were developed in response to various problems associated with Gerotor.RTM. gear sets (i.e., those in which the teeth of the internally toothed member are formed integrally therewith). Among the problems associated with Gerotor.RTM. gear sets was the extreme manufacturing precision required in the machining of the internally toothed member as well as the related problem of tooth-tip leakage and the resulting poor volumetric efficiency.
Although the development of Geroler.RTM. gear sets overcame or minimized many of the problems associated with Gerotor.RTM. gear sets, other problems still remained, and several new ones resulted. Among these is the extreme precision required in the machining of the rollers and pockets, especially as the axial length of the gear set increases. A problem which is associated with both Gerotor.RTM. and Geroler.RTM. gear sets is the extreme accuracy required in the valve timing. For example, in a motor, when the largest expanding volume chamber first begins to contract, if the valving to the exhaust line opens late there is a momentary pressure buildup within the contracting volume chamber such that the parts of the gear set are subjected to a stress, and upon opening of the valving, the builtup pressure may cause a shock wave in the exhaust line of several thousand psi or more, resulting in noisy operation and possible damage within the motor.